i) Field of the Invention
The present invention relates to a lubricant for refrigerator. More specifically, the present invention relates to a lubricant for refrigerators (including air conditioners) employing a chlorine-free Flon-type coolant such as Flon 134a (1,1,1,2-tetrafluoroethane), Flon 32 (difluoromethane), Flon 125 (1,1,1,2,2pentafluoroethane), Flon 143a (1,1,1-trifluoroethane), Flon 152a (1,1difluoroethane), Flon 134 (1,1,2,2-tetrafluoroethane) and the like, and a composition for refrigerators using said lubricant.
ii) Description of the Related Art
Flon-type coolants have conventionally been excellent for use as a coolant for refrigerators as they are chemically stable and have low toxicity. However, the recent Montreal Protocol decided that the use of chlorofluorocarbons, for example Flon 12 (dichlorodifluoromethane), among these Flon-type coolants shall be totally abolished by the year 2000, because chlorofluorocarbons is a cause of damage to the ozone layer in the stratosphere and contributes to global warming.
In such circumstances, Flon-type coolants not having chlorine in the molecules thereof, i.e. chlorine-free Flon-type coolants have been developed and are representatively illustrated by Flon 134a as an alternative to Flon 12.
However, because of the higher polarity thereof, these chlorine-free Flon-type coolants without chlorine in molecules thereof, such as Flon 134a and the like, have poor compatibility with naphthene mineral oils, alkylbenzene and the like which have been employed as lubricants for refrigerators. In order to improve the compatibility, therefore, polyalkylene glycol lubricants for refrigerators have been proposed as used in the Specification of U.S. Pat. No. 4,755,316, Japanese Patent Laid-Open No.3-28296 and like, while ester lubricants for refrigerators have been proposed as disclosed in Japanese Patent Laid-Open Nos.2-268068, 3-88892, 3-128991, 3-128992 and the like.
On the other hand, trace amounts of water and oxygen are present in refrigerator compressors, and the polyalkylene glycol refrigerator oils if used as a libricant are oxidized and deteriorated, resulting in a tendency for the acid value to increase; ester refrigerator oils if used as a lubricant are hydrolyzed to generate free acids and as such, they are not very practicable.
In order to improve the stability of the lubricants, Japanese Patent Application Nos.2-73649 and 2-64431 have proposed the use of glycidyl ether-type epoxy compounds which have good compatibility with Flon 134a and the like as a stabilizer.
However, these glycidyl ether-type epoxy compounds not only have such drawbacks that the products thereof inevitably involve chlorine residue which is not preferable environmentally, but the compounds are also so slow in the reaction with free acids and the like that the corrosive action of the free acids is not sufficiently suppressed.
Therefore, it is an object of the present invention to provide a lubricant for refrigerators, containing a stabilizer capable of reacting rapidly with free acids and having good compatibility with chlorine-free Flon-type coolants, such as Flon 134a.